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Measuring Variation

Scientific

Measurement of human variation can fall under the purview of several scholarly disciplines, many of which lie at the intersection of biology and statistics. The methods of biostatistics, the application of statistical methods to the analysis of biological data, and bioinformatics, the application of information technologies to the analysis of biological data, are utilized by researchers in these fields to uncover significant patterns of variability. Some fields of scientific research include the following:

Demography is a branch of statistics and sociology concerned with the statistical study of populations, especially humans. A demographic analysis can measure various metrics of a population, most commonly metrics of size and growth, diversity in culture, ethnicity, language, religious belief, political belief, etc. Biodemography is a subfield which specifically integrates biological understanding into demographics analysis.

In the social sciences, social research is conducted and collected data is analyzed under statistical methods. The methodologies of this research can be divided into qualitative and quantitative designs. Some example subdisciplines include:

• Anthropology, the study of human societies. Comparative research in subfields of anthropology may yield results on human variation with respect to the subfield's topic of interest.
• Psychology, the study of behavior from a mental perspective. Does a lot of experiments and analysis grouped into quantitative or qualitative research methods.
• Sociology, the study of behavior from a social perspective. Sociological research can be conducted in either quantitative or qualitative formats, depending on the nature of data collected and the subfield of sociology under which the research falls. Analysis of this data is subject to quantitative or qualitative methods. Computational sociology is also a method of producing useful data for studies of social behavior.

Anthropometry

Main article: Anthropometry

Anthropometry is the study of the measurements of different parts of the human body. Common measurements include height, weight, organ size (brain, stomach, penis, vagina), and other bodily metrics such as waist-hip ratio. Each measurement can vary significantly between populations; for instance, the average height of males of European descent is 178 cm ± 7 cm and of females of European descent is 165 cm ± 7 cm. Meanwhile, average height of Nilotic males in Dinka is 181.3 cm.

Applications of anthropometry include ergonomics, biometrics, and forensics. Knowing the distribution of body measurements enable designers to build better tools for workers. Anthropometry is also used when designing safety equipment such as seat belts. In biometrics, measurements of fingerprints and iris patterns can be used for secure identification purposes. As for forensics, patterns in anthropometry can be used to identify ancestry or race.

Measuring Genetic Variation

Human genomics and population genetics are the study of the human genome and variome, respectively. Studies in these areas may concern the patterns and trends in human DNA. The Human Genome Project and The Human Variome Project are examples of large scale studies of the entire human population to collect data which can be analyzed to understand genomic and genetic variation in individuals, respectively.

• The Human Genome Project is the largest scientific project in the history of biology. At a cost of $3.8 billion in funding and over a period of 13 years from 1990 to 2003, the project processed through DNA sequencing the approximately 3 billion base pairs and catalogued the 20,000 to 25,000 genes in human DNA. The project made the data available to all scientific researchers and developed analytical tools for processing this information. A particular finding regarding human variability due to difference in DNA made possible by the Human Genome Project is that any two individuals share 99.9% of their nucleotide sequences.
• The Human Variome Project is a similar undertaking with the goal of identification and categorization of the set of human genetic variation, specifically variations which are medically pertinent. This project will also provide a data repository for further research and analysis of disease. The Human Variome Project was launched in 2006 and is being run by an international community of researchers and representatives, including collaborators from the World Health Organization and the United Nations Educational, Scientific, and Cultural Organization.

Genetic Drift

Main article: Genetic Drift

Genetic drift is one method by which variability occurs in populations. Unlike natural selection, genetic drift occurs when alleles decrease randomly over time and not as a result of selection bias. Over a long history, this can cause significant shifts in the underlying genetic distribution of a population. We can model genetic drift with the Wright-Fisher model. In a population of N with 2N genes, there are two alleles with frequencies p and q. If the previous generation had an allele with frequency p, then the probability that the next generation has k of that allele is:

${2N \choose k}p^{k}q^{2N-k}$

Over time, one allele will be fixed when the frequency of that allele reaches 1 and the frequency of the other allele reaches 0. The probability that any allele is fixed is proportional to the frequency of that allele. For two alleles with frequencies p and q, the probability that p will be fixed is p. The expected number of generations for an allele with frequency p to be fixed is:

${\bar {T}}_{\text{fixed}}={\frac {-4N_{e}(1-p)\ln(1-p)}{p}}$

Where N_e is the effective population size.

Single-nucleotide polymorphism

Main article: Single-nucleotide polymorphism

Single-nucleotide polymorphism or SNPs are variations of a single nucleotide. SNPs can occur in coding or non-coding regions of genes and on average occur once every 300 nucleotides. SNPs in coding regions can cause synonymous, missense, and nonsense mutations. SNPs have shown to be correlated with drug responses and risk of diseases such as sickle-cell anemia, Alzheimer's disease, cystic fibrosis, and more.

DNA Fingerprinting

Main article: DNA Fingerprinting

DNA profiling, whereby a DNA fingerprint is constructed by extracting a DNA sample from body tissue or fluid. Then, it is segmented using restriction enzymes and each segment marked with probes then exposed on X-ray film. The segments form patterns of black bars;the DNA fingerprint. DNA Fingerprints are used in conjunction with other methods in order to individuals information in Federal programs such as CODIS (Combined DNA Index System for Missing Persons) in order to help identify individuals

Mitochondrial DNA

Mitochondrial DNA, which is only passed from mother to child. The first human population studies based on mitochondrial DNA were performed by restriction enzyme analyses (RFLPs) and revealed differences between the four ethnic groups (Caucasian, Amerindian, African, and Asian). Differences in mtDNA patterns have also been shown in communities with a different geographic origin within the same ethnic group

Alloezymic Variation

Alloenzymic variation, a source of variation that identifies protein variants of the same gene due to amino acid substitutions in proteins. After grinding tissue to release the cytoplasm, wicks are used to absorb the the resulting extract and placed in a slit cut into a starch gel. A low current is run across the gel resulting in a positive and negative ends. Proteins are then separated by charge and size, with the smaller and more highly charged molecules moving more quickly across the gel. This techniques does underestimate true genetic variability as there may be an amino acid substitution but if the amino acid is not charged differently than the original no difference in migration will appear it is estimated that approximately 1/3 of the true genetic variation is not expressed by this technique.

Structural Variation

Structural variation, which can include insertions, deletions, duplications, and mutations in DNA. Within the human population, about 13% of the human genome is defined as structurally variant.

Phenotypic Variation

Further information: Phenotype § Phenotypic_variation

Phenotypic variation, which accounts for both genetic and epigenetic factors that affect what characteristics are shown. For applications such as organ donations and matching, phenotypic variation of blood type, tissue type, and organ size are considered.

Civic

Measurement of human variation may also be initiated by governmental parties. A government may conduct a census, the systematic recording of an entire population of a region. The data may be used for calculating metrics of demography such as sex, gender, age, education, employment, etc; this information is utilized for civic, political, economic, industrial, and environmental assessment and planning.

Commercial

Commercial motivation for understanding variation in human populations arises from the competitive advantage of tailoring products and services for a specific target market. A business may undertake some form of market research in order to collect data on customer preference and behavior and implement changes which align with the results.

Bibliography

• Tian, Jianjun Paul (2008). Evolution Algebras and their Applications. Lecture Notes in Mathematics. Vol. 1921. Berlin; New York: Springer. doi:10.1007/978-3-540-74284-5. ISBN 978-3-540-74283-8. LCCN 2007933498. OCLC 173807298. Zbl 1136.17001.
• Hedrick, Philip W. (2005). Genetics of Populations (3rd ed.). Boston, MA: Jones and Bartlett Publishers. ISBN 0-7637-4772-6. LCCN 2004056666. OCLC 56194719.

References